1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) panel. More particularly, the present invention relates to an active device array substrate and a driving method thereof.
2. Description of Related Art
Presently, the performance of thin film transistor liquid crystal display (TFT-LCD) is proceeding towards high contrast ratio, no gray level inversion, low color shift, high luminance, high color richness, high color saturation, quick response, and wide viewing angle etc. Existing techniques for achieving wide viewing angle include twisted nematic (TN) liquid crystal plus wide viewing film, in-plane switching (IPS) LCD, fringe field switching LCD, and multi-domain vertically alignment (MVA) TFT-LCD etc.
Take a conventional MVA-LCD panel as example, the alignment protrusions or slits formed on the color filter substrate or TFT array substrate allow liquid crystal molecules to be arranged in different directions so that a plurality of different alignment domains can be obtained. Thus, wide viewing angle can be achieved by the MVA-LCD panel.
FIG. 1 illustrates the relationship between the normalized transmittance and the gray level of a conventional MVA LCD panel. Referring to FIG. 1, the abscissa indicates gray level and the ordinate indicates normalized transmittance. As shown in FIG. 1, even though the conventional MVA-LCD panel can achieve a wide viewing angle, the transmittance-level curve has different curvatures along with the changes of the viewing angle. In other words, when the viewing angle changes, the brightness displayed by the conventional MVA-LCD also changes, so that the color shift or color washout may be produced.
Various conventional techniques have been provided for resolving the issue of color shift or color washout. One of the methods is to form an extra capacitor in a single pixel unit. Different pixel electrodes in the single pixel unit respectively produce different electric fields through capacitance coupling, so that the liquid crystal molecules above the different pixel electrodes have different arrangements. Even though color shift is reduced, such method may cause reduction in the display quality due to the RC delay effect thereof.
Another method is to add a transistor in each pixel unit. In other words, each single pixel unit has two transistors. With these two transistors, two pixel electrodes in a single pixel unit produce two different electric fields so that the liquid crystal molecules above the pixel electrodes have different arrangements and accordingly color shift is reduced. However, in this method, two transistors have to be formed in a single pixel unit and the number of scan lines or data lines has to be increased, therefore both the complexity of the driving circuit and the fabricating cost thereof are increased.
Other conventional techniques for reducing color shift, such as U.S. Pat. No. 6,486,930, U.S. Pat. No. 6,933,910, and U.S. Pat No. 2005/0200788 etc, have been disclosed. For example, a pixel unit array structure provided in US 2005/0200788 can reduce color shift without increasing the number of scan lines or data lines; however, a more complex driving method has to be adopted in this patent to allow two pixel electrodes in a single pixel unit to produce different electric fields. Specifically, in U.S. 2005/0200788, the data signals to be inputted into the same pixel unit are not outputted continuously; therefore a memory has to be installed in the driving circuit in order to reorder the output data signals. Such design increases both the complexity of signal processing and the fabricating cost of the driving circuit.